RU2215050C1 - Method of refining ore raw material and device for realization of this method - Google Patents

Abstract

FIELD: metallurgy; ecologically pure process of production of magnesium from dolomite raw material and other valuable metals or metalloids possessing toxicity and self- ignition capacity in oxidizing medium. SUBSTANCE: proposed method includes grinding and mixing of ore material with powder of iron alloys containing 45 to 75% of silicon followed by compacting mixture in briquettes. Fragments of magneto-conducting metals are placed between layers. Then, furnace is sealed-up and evacuated at residual pressure of from 0.1 to 1.0 mm Hg, after which vacuum silicothermal reduction is performed in the course of contact heating of briquettes from fragments of magneto-conducting materials. After reduction, condensate of low- melting product is molten for obtaining cast blank and ore residue is withdrawn from furnace. Device includes vacuum induction furnace with bottom, ore reside receiving unit, condenser, auxiliary hermetic reservoir with ingot and external heater and molten metal seals which contain medium at melting point of 90 to 130 C. Bottom is hermetically connected with furnace and condenser is hermetically connected with furnace and auxiliary reservoir by means of molten metal seals. EFFECT: increased specific productivity due to reduction of technological processes; reduced labor consumption; enhanced reliability and fire protection. 4 cl, 1 dwg, 2 tbl, 1 ex

Description

 The invention relates to the metallurgy of low-melting metals or metalloids, for example, to the environmentally friendly production of magnesium from ubiquitous dolomite raw materials, the safe production of phosphorus from phosphorites for the production of fertilizers in the chemical industry, as well as other valuable metals or metalloids characterized by toxicity and the ability to spontaneous combustion in an oxidizing environment.

 Analogues of the first object of the proposed invention are a method of metallothermal reduction of ore raw materials, including the placement and heating of a mixture of reactants in lined reactors or retorts made of heat-resistant steel (Samsonov G.V., Perminov V.P. Magnetermia. M., Metallurgy, 1971, p. 137 -171), as well as a method for the reduction of magnesium from its oxide by silicoaluminium in electric furnaces without using a vacuum (RU 2149198 C1, 06/14/2002).

 The disadvantages of these methods are low productivity due to the slow indirect heating of the charge and high energy consumption.

 The prototype of the first object of the proposed invention is a method for the redistribution of ore raw materials containing compounds of low-melting metal - magnesium, based on metallothermal reduction of magnesium in a vacuum by silicoaluminium from a mixture of magnesium and calcium oxides (Strelets Kh.L., Taits A.Yu., Gulyanitsky B.S. Metallurgy of Magnesium. M., Metallurgizdat, 1960, p.332).

 The disadvantages of this method are low productivity due to the slow indirect heating of the charge and energy consumption, as well as the cost of the method due to the use of an expensive reducing agent - silicoaluminum.

 An analogue of the second object of the proposed invention is a device for producing magnesium, containing a single-phase sealed electric furnace with graphite electrodes, lined with magnesite brick. The furnace is connected by a vacuum system to a condensation chamber and to a mold (RU 2149198 C1, 06/14/2002).

 The disadvantages of the device are the short-term resource of the equipment, the complexity and danger of maintenance and high energy consumption.

 The prototype of the second object of the proposed invention is a device for the redistribution of ore raw materials containing compounds of low-melting metal - magnesium, including a sealed electric vacuum furnace with graphite electrodes, lined with magnesite brick. The furnace is connected by a vacuum system to a condensation chamber and to a mold (Strelets Kh.L., Taits A.Yu., Gulyanitsky BS. Metallurgy of magnesium. M., Metallurgizdat, 1960, p.332).

 The disadvantages of this device are also the short-term resource of the equipment, the complexity and danger of maintenance and high energy consumption.

 In the first aspect of the invention, a technical result is achieved by increasing the specific productivity by reducing the number of technological operations while significantly reducing labor costs, reducing energy costs, obtaining a fusible product of higher purity, increasing fire and environmental safety of production by changing the technological scheme, reducing the technological time cycle by reducing heating time.

 The specified technical result is achieved as follows.

 The method of redistribution of ore raw materials containing compounds of fusible metals or metalloids, is that the crushed ore raw materials are mixed with a powder of iron alloys containing 45-75% silicon.

 The mixture is compacted into briquettes, which are loaded in layers into a vacuum induction furnace. Fragments of magnetically conductive metals are placed between the layers. Then carry out the sealing of the furnace and its evacuation at residual pressures from 0.1 to 1.0 mm RT.article. Vacuum silicothermal reduction of ore raw materials is carried out in the furnace in the process of contact heating of briquettes from fragments of magnetically conductive metals heated by Foucault currents to temperatures ensuring the maximum evaporation rate of a low-melting product without overheating of its vapor. After completion of the recovery, the condensate of the low-melting product is melted to obtain a cast billet, and the ore residue is removed from the furnace.

 Fragments of magnetic metals are used in an amount of 20-40 wt.% By weight of the mixture.

 The condensate of the fusible product is melted in an inert medium when heated to a temperature 10-15% higher than the melting point of the fusible product.

 In the second object of the invention, a technical result is achieved, which consists in increasing the reliability of the equipment due to the repeated use of the furnace lining, increasing the productivity of the device and reducing its energy consumption.

 The specified technical result is achieved as follows.

 A device for the redistribution of ore raw materials containing compounds of fusible metals or metalloids, includes a vacuum induction furnace with a bottom. The bottom is installed with the ability to move relative to the guide racks of the ore residue receiving unit and hermetically sealed to the casing of the vacuum induction furnace using a liquid metal shutter.

The device also contains a capacitor mounted above the casing of the vacuum induction furnace with the possibility of moving relative to it and a sealed auxiliary tank and sealed articulation with them using liquid metal gates. The auxiliary tank is equipped with a mold and an external heater. All liquid metal gates contain a medium with a melting point of 90-130 ^o C.

 The invention is illustrated by the drawing, which schematically shows the proposed device for the redistribution of ore raw materials containing compounds of low-melting metals or metalloids.

 The drawing shows a vacuum induction furnace 1 with an inductor 2 and a bottom 3. The bottom 3 is mounted with the possibility of movement relative to the guide posts 4 of the ore residue receiving unit 5, equipped with a pusher 6 of the ore residue, dumping it, for example, into a grinding device. The bottom 3 is hermetically articulated with the casing of the vacuum induction furnace 1 using a liquid metal shutter 7.

The device also contains a condenser 8 with cooling 9 with an adjustable cooling rate, designed to collect the sublimation of the low-melting product 10. The condenser 8 is mounted above the housing of the vacuum induction furnace 1 with the possibility of movement and rotation relative to it and a sealed auxiliary tank 11 using the mechanism 12 of the movement and rotation and tight joints with them using liquid metal shutters 13, 14. The auxiliary tank 11 is equipped with a mold 15 and an external heater 16. All liquid metal shutters Orae 7, 13, 14 comprise a medium with a melting point of 90-130 ^o C.

 In the upper part of the furnace 1 there is a thermal perforated screen 17 and a vacuum pipe 18 for venting gases. Inside the furnace 1, briquettes of processed raw materials are loaded in layers, and fragments 19 of magnetically conductive metals are placed between the layers. The drawing also shows the bottom 3 in the unloading position of the ore residue 20 after the recovery process.

 The method of redistribution of ore raw materials containing compounds of fusible metals or metalloids using the proposed device is as follows.

 A stoichiometric mixture of crushed ore raw materials containing compounds of low-melting metals or metalloids and a reducing agent in the form of a powder of iron alloys with 45-75 wt.% Silicon (ferrosilicon) is compacted into briquettes, which are layer by layer loaded into a vacuum induction furnace 1. Fragments 19 of magnetic conductive metals in an amount of 20-40 wt. % of the mass of briquettes. Loaded in this way, the furnace furnace 1 is sealed and vacuum silicothermic reduction of the ore material is started.

 The mixture is heated to temperatures ensuring the maximum evaporation rate of the low-melting product without overheating of its vapor, with a pressure in the furnace volume of 1 from 0.1 to 1.0 mm Hg. achieved due to Foucault currents, which are generated by the inductor 2 in the magnetically conductive components - fragments 19 and ferrosilicon, which in turn contact heat the ore raw materials.

 Thus, the heating of the non-magnetic part of the charge is achieved due to the presence in it of chemically passive fragments 19 of magnetically conductive metals having high heat and magnetic conductivity. This technique significantly reduces the cost of the furnace unit, since it eliminates the need for heat-resistant alloys or expensive refractories for lining vacuum furnaces, and also reduces the production time for heating the charge and ensures uniform heating.

 With a decrease in the fraction of fragments 19 of less than 20%, the charge heating time increases more than twofold. An increase in the proportion of more than 40% reduces the share of ore raw materials and 1.3-1.5 times reduces the yield of volatile product.

 Using vacuum allows you to reduce the estimated amount of reducing agent and increase the yield of volatile product while reducing costs.

 Vapors of a volatile product formed during heating of the charge are discharged from the furnace 1 through the screen 17 into the condenser 8 with cooling 9.

 The sealed capacity of the furnace 1 is purged with nitrogen in order to accelerate the cooling of pyrophoric products.

Then the shutter 13 is melted and, using the mechanism 12, the condenser 8 is raised in the upper position by 180 ^° and the auxiliary tank 11 is introduced into the shutter 11. Using the external heater 16, the walls of the condenser 8 are heated to a temperature 10-15% higher than the melting temperature low-melting product, and melting of the condensate of the low-melting product in an inert medium. The molten product flows into the mold 15, where a cast billet is formed.

In order to increase the reliability of sealing-depressurization of elements in the device, liquid metal shutters 7, 13, 14 filled with Pb-Bi alloy (mp 130 ^° C), equipped with heaters and a cooling system that are remotely controlled, are used. At the necessary moments of the technological process, the medium filling the gates 7, 13, 14 is melted, which allows the bottom 3 and the condenser 8 of the furnace 1 to be moved.

 Lowering the bottom 3 of the furnace 1 to the lower position ensures the extraction of ore residue from the conical crucible of the furnace 1, and a remote, double rotation of the bottom 3 leads to the discharge of materials onto the grate in order to separate the magnetic (steel) fraction suitable for recycling by remelting to obtain valuable commercial products in in the form of castings from ductile iron.

Example
As ore raw materials, materials containing calcined dolomite with the addition of ferrosilicon as a reducing agent are used.

Проведенные опыты позволили установить оптимальный температурный режим зависимости выхода магния (% от теоретического) от температуры процесса. (Таблица 1). Нижний температурный предел отвечает началу твердофазного взаимодействия материалов шихты. Максимальная скорость процесса достигается при температурах 1200-1500^oС. Однако увеличение температуры сверх 1400±50^oС приводит к резкому увеличению скорости процесса, увеличению количества перегретых паров магния, которые осаждаются, помимо конденсатора, также на элементах конструкции печи, что приводит к безвозвратным потерям продукта и снижению его выхода. Из этих данных следует, что оптимальным для проведения способа является температурный интервал 1200-1350^oС.Into a conical crucible of a vacuum induction furnace 1 with an internal diameter of ≈800 mm, a height of ≈1200 mm, and a volume of ≈600 l, made of heat-resistant cement, 400 kg (50 l) and 1.5 t (500 l) of briquettes are scrap-loaded with ferrous metals a stoichiometric mixture of calcined dolomite with 45% ferrosilicon in a ratio of 24: 7 mass parts. Induction heating of fragments of a charge of magnetically conductive metals is carried out to 1300-1450 ^o C and contact briquettes are heated to 1200-1350 ^o C at a residual pressure of 0.1 to 1.0 mm Hg in order to develop a vacuum silicothermic reduction reaction:

The experiments performed allowed us to establish the optimal temperature regime for the dependence of the yield of magnesium (% of theoretical) on the process temperature. (Table 1). The lower temperature limit corresponds to the onset of solid-phase interaction of the charge materials. The maximum process speed is achieved at temperatures of 1200-1500 ^o C. However, an increase in temperature in excess of 1400 ± 50 ^o C leads to a sharp increase in the process speed, an increase in the number of superheated magnesium vapor, which are deposited, in addition to the condenser, also on the structural elements of the furnace, which leads to irrevocable product losses and reduced yield. From these data it follows that the optimal temperature for the method is the temperature range 1200-1350 ^o C.

The chemical inertness of iron scrap is confirmed by thermodynamic calculations. For silicothermal reduction reactions of calcined dolomite with the formation of iron silicates (type Fe ₂ SiO ₄ , Fe ₃ SiO ₅ ) and even iron-calcium silicate (reaction 1) and calcium silicate (reaction 2), the Gibbs energy is of great positive value in the temperature range under consideration, i.e. e. these reactions are not carried out (see Table 2). The reactions taking place with the formation of complex calcium-magnesium silicates with the lowest Gibbs energy have a thermodynamic advantage.

An important feature of the proposed method is the change in the quality of the reducing agents when using powdered ferrosilicon and the use of vacuum. In the known methods, burnt dolomite is used in the charge, and ferrosilicon is used as a reducing agent without the use of additives of fragments from magnetically conductive metals (steel scrap) and vacuum. It is believed that the process develops according to reaction 2 (see Table 2). This requires an increase in the cost of an increased amount of ferrosilicon according to the stoichiometry of the reactions (see the list of reactions in Table 2), leads to a decrease in the proportion of magnesium oxide in the charge and, therefore, to a decrease in the yield of magnesium sublimates. The calculations in Table 2 show that in the recovery process according to the proposed method, reactions 3 and 4 are carried out, having minimal Gibbs energy ΔG ^o . Consequently, the estimated amount of reducing agent decreases and the yield of magnesium increases while reducing costs. In addition, thermodynamic estimates in the ideal gas approximation confirm that the use of vacuum increases the yield of magnesium sublimates.

 Next, ≈170 kg of magnesium vapor, which is formed by heating the mixture by reaction 4, is taken into a cooled condenser and the hermetic capacity of the furnace is purged with nitrogen to accelerate the cooling of pyrophoric products.

 Liquid metal shutters 13, 14 are melted, the capacitor 8 is turned and hermetically connected to the auxiliary tank 11 for non-oxidative melting of magnesium crystals (drusen).

 The liquid metal shutter 7 is melted, the bottom 3 of the furnace 1 with the cake mixture is lowered and the latter is dumped into the grinding device for the purpose of subsequent separation of the metal and oxide phases.

The hermetic condenser 8 is heated by an external heater 16 to a temperature of 670-680 ^o C, crystallization of liquid magnesium is carried out in a conical mold 15 and an ingot weighing ≈170 kg (9.8 l) is removed.

 The bottom 3 is returned to the standard position, hermetically connected to the furnace body 1 and a fresh portion of the charge is loaded.

 Return the capacitor 8 to its original position, hermetically connect it to the furnace body 1 and thus prepare the device for the next cycle.

 The invention ensures the safe production of, for example, magnesium in an amount of 0.65-0.70 t / day (250 t / year), and to maximize the fire safety level, the furnace and sublimation units can be placed in a stand-alone protective chamber.

 The most cost-effective use of mini-complexes equipped with a group of 4-8 proposed devices and equipment for the disposal of technological waste.

 In the considered specific example, the yield of steel fragments reaches 0.44 t per operation or 1.75 t / day, and remelting, carburizing and metal modification in an auxiliary furnace serving the group of the proposed devices allows to obtain up to 1.85 t (2.6 t / t Mg) chill castings of ductile iron with spherical graphite, the cost of which reaches 35-45% of the cost of the main product (magnesium ingots).

 Waste in the form of calcium silicate (see reaction 4) in an amount of up to 0.6 tons per operation is used as filler (30%) of concrete mix (2.0 tons) in the manufacture of building blocks, which eliminates the formation of dumps and gives an additional economic effect .

 Comparison of the invention with traditional technology shows that, in addition to a radical increase in the level of environmental and fire safety, there is a decrease in the cost of the main product by 30-40%.

Claims (4)

 1. The method of redistribution of ore raw materials containing compounds of low-melting metals or metalloids, which consists in the fact that the crushed ore raw materials are mixed with a powder of iron alloys containing 45-75% silicon, compact the mixture into briquettes, which are layer by layer loaded into a vacuum induction furnace, while fragments of magnetically conductive metals are placed between the layers, after which the furnace is sealed and evacuated at residual pressures of 0.1 to 1.0 mm Hg. Art. and vacuum silicothermal reduction of the ore material is carried out during contact heating of the briquettes from fragments of magnetically conductive metals heated by Foucault currents to temperatures ensuring the maximum rate of evaporation of the low-melting product without overheating of its vapor, after completion of the recovery, the condensate of the low-melting product is melted to obtain a cast billet, and the ore residue removed from the oven.  2. The method according to p. 1, characterized in that fragments of magnetically conductive metals are used in an amount of 20-40% by weight of the mixture.  3. The method according to p. 1, characterized in that the condensate is melted of the low-melting product in an inert medium when heated to a temperature 10-15% higher than the melting temperature of the low-melting product. 4. A device for the redistribution of ore raw materials containing compounds of fusible metals or metalloids, containing a vacuum induction furnace with a bottom mounted to move relative to the guide racks of the ore residue receiving unit and hermetically coupled to the housing of the vacuum induction furnace using a liquid metal shutter, and a capacitor installed above the casing of the vacuum induction furnace with the ability to move and rotate relative to the casing of the vacuum induction furnace and a sealed auxiliary burning capacity, equipped with a mold and an external heater, and hermetically articulated with them using liquid metal gates, and all liquid metal gates contain a medium with a melting point of 90-130 ^o C.

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